Polyamide acids and polyimides prepared from a mixture of polycarboxylic acid anhydrides

ABSTRACT

DISCLOSED HEREIN ARE POLYMERIC MATERIALS CHARACTERIZED BY HAVING A PLURALITY OF RECURRING IMIDE LINKAGES AND DIRECT LINKAGES BETWEEN AROMATIC NUCLEI. THESE MATERIALS ARE THE POLYMERIC REACTION PRODUCT OF (1) A POLYCARBOXYLIC ANHYDRIDE HAVING A MOLECULAR STRUCTURE COMPRISING AT LEAST TWO UNITS (D) EACH DERIVED BY THE LOSS OF ONE OR MORE HYDROGEN ATOMS FROM THE NUCLEUS OF AN AROMATIC CARBOXYLIC ANHYDRIDE AND AT LEAST ONE UNIT (E) DERIVED BY THE LOSS OF TWO OR MORE HYDROGEN ATOMS FROM THE NUCLEUS OR THE NUCLEI OF AN AROMATIC COMPOUND CONTAINING ONE OR MORE NUCLEI, AND WHEREIN ANY D UNIT IS LINKED DIRECTLY TO ONE OR MORE E UNITS AND ANY E UNIT IS LINKED DIRECTLY TO AT LEAST TWO UNITS SELECTED FROM D UNITS AND B UNITS, WITH (2) A POLYAMINE CONTAINING TWO OR MORE PRIMARY AMINO GROUPS PER MOLECULE.

United States Patent Office POLYAMIDE'ACDS AND POLYIMIDES PREPARE YFROM A MIXTURE F .POLYCARBOXYLIC ACID ANHYDRIDES Frank Long, Wrexham, and Gordon Roy Ensor, Elangollen, Wales, assignorsto Monsanto Chemicals -.,-Limited,. London, England, a British company No Drawing. Filed Jan. 29, 1968, Ser. No. 701,103 Claims priority, application Great Britain, Feb. 3, 1967, p 5,362/67 Int. Cl. C08g 20/32 s; (31.260 47 12 Claims ABSTRACTQF DISCLOSURE QDisclosed herein are polymeric materials characterized by havingfa plurality of recurring imide linkages and directli'nkages between aromatic nuclei. These materials are the polymeric, reaction productof 1) a polycarboxylic anhydride having a-inolecular structure comprising at least two units.(D-) each derived by the loss of one ormore hydrogen atoms from the nucleus of an aromatic carboxylic anhydride and at least one unit (E) derived by the loss of. two or more hydrogen atoms from the nucleus or the nuclei of an aromatic compound containing one or. more nuclei, and wherein any D unit is linked directly to one or more E. units and any E unit is linked directly to at least two units selected from D units and B units,. witl1 2) a polyamine containing two or more primary amino groups per molecule.

'ICIROSS-REFERENICESYTO RELATED V APPLICATIONS firms application claims the rightof priority of British patent application No. 5,362/67, filed Feb. 3, 1967.

'- BACKGROUND OF THE INVENTION l (1) Field of the invention This invention relates to'novel polymeric materials. More particularly, this invention relates to novel polymeric materials characterized by having a plurality of recurring imide linkages and direct linkages between aromatic nuclei. These materials are the polymeric reaction product of (1) a. polycarboxylic anhydride having a molecular structure comprising at least two units (D) each derived by the loss of one or more hydrogen atoms from the nucleus of an aromatic carboxylic anhydride and at least one unit (E)" derived by'the loss of two or more hydrogen atoms from the nucleus or the nuclei of an aromatic compound containing one or more nuclei, and wherein any D unit is linked directly to one or more E units and any E unit is linked directly to at least two units selected from D unitsand E units; with (2) a polyamine containing two or more primary amino groups per molecule. l

(2) Description of the prior art Polymeric Compositions containing a plurality of recurring imide linkages are Well known in the art as is evidenced by US. Patents 3,179,633, 3,179,634, 3,179,635, 3,190,856'and others. The polymers described inthe foregoing references are characterized .by having good. thermal stability and other physical properties. 'How Patented Jan. 12, 1 971 2 SUMMARY OF THE INVENTION This invention relates to novel polymeric materials characterized by having a plurality of recurring imide linkages and direct linkages between aromatic nuclei. These materials are the polymeric reaction product of (1) a polycarboxylicanhydride having a molecular structure comprising at least two units (D) each derived by the loss of one or more hydrogen atoms from the nucleus of an aromatic carboxylic anhydride and at least one unit (E) derived by the loss of two or more hydrogen atoms from the nucleus or the nuclei of an aromatic compound containing one or more nuclei, and wherein any D unit is linked directly to one or more E units and any E unit is linked directly to at least two units selected from D units and E units, with (2) a polyamine containing two or more primary amino groups per molecule.

This invention solves a problem of long standing in the art by providing polymeric materials with high thermal and oxidative stability which are suitable for use in the fabrication of articles that are required to withstand prolonged periods of service at high temperatures.

It is therefore an objectof this invention to provide new polymeric materials having high thermal and oxidative stability.

It is another object of this invention to provide a process for the production of new polymeric materials having high thermal and oxidative stability.

The foregoing and other objects are obtained by the reaction. of (1) a polycarboxylic anhydride having a molecular structure comprising at least two units (D) each derived by the loss of one or more hydrogen atoms from the nucleus of an aromatic carboxylic anhydride and at least one unit (E) derived by the loss of two or more hydrogen atoms from the nucleus or the nuclei of an aromatic compound containing one or more nuclei, and wherein any D unit is linked directly to one or more E units and any E unit is linked directly to at least two units selected from D units and E units, with (2) a polyamine containing two or more primary amino groups per molecule.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The polycarboxylic anhydrides for use as starting mate rials in the production of the polymers of the present invention are those described in British Patent Specificaever, the increasing demands of modern technology requires new polymeric materials with superior properties. A problem exists in the art in providing new polymeric materials with-superior physical propertieswhich will meet the requirements of modern technology."

tion No. 12,466/67.

The polycarboxylic anhydride is usually one in which the unit D is derived by the loss of one or more hydrogen atoms from the nucleus of an aromatic carboxylic monoanhydride, for example phthalic anhydride, and the unit E is typically derived from benzene. Thus in one of the simplest instances, the polycarboxylic anhydride is terphenyl'tetracarboxylic dianhydride where two phthalic anhydride units are linked through a benzene nucleus. Particularly useful as polycarboxylic anhydrides from which the polymers of the invention are derivable are mixtures of aromatic polyanhydrides wherein the individual anhydrides can be represented by the formula D E "where D represents a radical derived by the loss of one or more hydrogen atoms from the nucleus of the phthalic anhydride molecule, E represents a radical derived "by the loss of two or more hydrogen atoms from the benzene molecule, and x and y are integers.

The overall ratio. of D units to E units in the mixture can vary over a wide range, but generally the most use.- ful' are those in which the ratio of D units to E units is from lz2 to 2:1 and more especially from 1:1 to 2:1.

In many of the individual anhydrides, xhas a value which is 1 greater than the value of y, and in general, individual anhydrides of this type range from those containing two D units to one B unit, i.e. terphenyl tetracarboxylic dianhydride, referred to above, to those containing eleven D units to ten E units.

The simplest polycarboxylic anhydride may be represented by the following general formula:

DED (I) Some more complex polycarboxylic anhydrides may be represented by the following general formula:

E I I l D D D (III) Mixtures of anhydrides represented by the foregoing formulae are especially useful.

Polycarboxylic anhydride starting materials used in the present invention are obtained by heating an aromatic polysulphonyl halide with an aromatic carboxylic anhydride under conditions such that sulphur dioxide and a hydrogen halide are evolved and direct linkages are formed between carbon atoms of the nucleus that was originally the nucleus of the aromatic polysulphonyl halide and carbon atoms of the nuclei that were originally carboxylic anhydride nuclei.

The aromatic sulphonyl halide used in the production of a polyanhydride are compounds containing one or more aromatic nuclei, and where it contains more than one nucleus, the sulphonyl halide groups are linked to carbon atoms of the same nucleus or to carbon atoms of different nuclei. A preferred class of polynuclear aromatic sulphonyl halides are those that contain from two to four aromatic nuclei arranged in a sequence, successive nuclei in the sequence being linked directly or through an intermediate atom or group, for example an oxygen or sulphur atom, or a carbonyl or sulphonyl group.

The nucleus or nuclei in the sulphonyl halide can be carbocyclic or heterocyclic, but carbocyclic nuclei, such as for instance benzene or naphthalene nuclei, are usually preferred. Useful properties are, however, also associated with nuclei having a heterocyclic ring fused to one or more carbocyclic rings, for example dibenzothiophen or dibenzofuran nuclei. Thus the sulphonyl halide can, for example, be a sulphonyl halide derivative of benzene; naphthalene; a polyaryl, especially a polyphenyl such as for instance biphenyl or terphenyl; an aryl ether, especially a phenyl ether, for example diphenyl ether or a bis- (phenoxy)benzene; an aryl sulphide or sulphone, for example diphenyl sulphide, a dinaphthyl sulphide or diphenyl sulphone; dibenzothiophene; or of dibenzofuran.

The nucleus or nuclei of the aromatic sulphonyl halide can contain one or more substituents in addition to the sulphonyl halide groups. Such a substituent can be selected from a range of atoms or groups, including for instance halogen atoms, alkyl groups and alkoxy groups. In this respect, however, preferred polyanhydrides are those derived from unsubstituted aromatic sulphonyl halides or from aromatic sulphonyl halides having one or more fluorine or chlorine atoms as additional nuclear substituents.

The sulphonyl halides usually employed in practice are the sulphonyl chlorides although the sulphonyl bromides, for example, can also be used.

Specific examples of suitable aromatic sulphonyl halides are: benzene-1,3-disulphonyl chloride; benzene-1,3-disulphonyl bromide; 2,4,5,6 tetrachlorobenzene 1,3 disulphonyl chloride; naphthalene 1,5-disulphonyl chloride; naphthalene-2,7-disulphonyl chloride; naphthalene-1,3,6- trisulphonyl chloride; diphenyl-4,4'-disulphonyl chloride; diphenyl ether-4,4'-disulphonyl chloride; diphenyl sulphide-4,4'-disulphonyl chloride; dibenzothiophen-2,8-disulphonyl chloride and dibenzofuran-3,7-disulphonyl chloride.

The aromatic carboxylic intramolecular anhydride that is used in the production of a polyahydride can contain one or more anhydride groups, one or more aromatic nuclei, and, consistent with the requirement that nuclear hydrogen atoms should be present and that the anhydride should otherwise be inert with respect to the sulphonyl halide, one or more nuclear substituents. Such optional substituents include halogen atoms, for example, fluorine, chlorine or bromine.

The nucleus or each nucleus of the aromatic anhydride is generally carbocyclic, for instance a benzene or naphthalene nucleus, although desirable properties are also associated with nuclei having a heterocyclic ring fused to one or more carbocyclic rings, for example dibenzothiophen or dibenzofuran nuclei. Where more than one aromatic nucleus is present, these can be linked to each other directly or indirectly, for example through an oxygen or sulphur atom, or through an alkylene, carbonyl or sulphonyl group.

Aromatic anhydrides containing more than one anhydride grouping are preferably compounds that also contain more than one aromatic nucleus, such that only one anhydride grouping is associated with any one nucleus.

The preferred aromatic anhydride for use in the present invention is phthalic anhydride. Examples of others that can be used are the monochlorophthalic anhydrides; the phenylphthalic anhydrides; naphthalic anhydride; 3,3',4, 4'-biphenyl tetracarboxylic dianhydride; benzophenone 3,3,4,4-tetracarboxylic dianhydride; and diphenyl sulphone 3,3,4,4-tetracarboxylic dianhydride.

In the above process for the production of a polyanhydride starting material, it is usual to use a molar excess of the aromatic carboxylic anhydride, and preferably at least one mole of the anhydride per equivalent of the polysulphonyl halide (equivalent weight=molecular Weight divided by the number of sulphonyl halide groups). It is sometimes advantageous to use a relatively large excess of the anhydride, for example up to 20 moles per mole of polysulphonyl halide. Unreacted anhydride is recovered from the reaction mixture after the evolution of sulphur dioxide and hydrogen halide is substantially complete. The reaction temperature in the produc tion of the polycarboxylic anhydride usually lies Within the range 200 to 350 C., although the reaction can proceed at temperatures outside these limits, for example from to 200 or from 350 to 500 C. Where the boiling point of the aromatic carboxylic anhydride permits, it is usually most convenient to boil the reaction mixture under reflux at atmospheric pressure, thus giving, in the case of phthalic anhydride, reaction temperatures of from 275 to 320 C.

The ratio of benzene disulphonyl halide to phthalic anhydride employed in preparing the preferred polycarboxylic anhydride depends on the proportion of anhydride (D) units required in the product. It is found that under normal process conditions, i.e. operating at atmospheric pressure at temperatures in the range 200-350 C., not all the phthalic anhydride is utilized, so that the ratio of phthalic anhydride to benzene disulphonyl halide in the reaction mixture should exceed the ratio of D units to E units required in the product. The exact ratio of reactants to be used to achieve a particular ratio of units in the product will depend on the particular reaction temperature and the presence or absence of a catalyst, but except for the production of a product consisting largely or exclusively of terphenyl dianhydrides it appears that generally the molar ratio of phthalic anhydride to benzene disulphonyl halide in the reaction mixture should be from approximately 1.5 to 5 times the ratio of corresponding units in the product. Within this range,'the required excess increases as the ratio of D units to E units required in the product approaches 2: 1. Where the required product consists largely or exclusively of terphenyl tetracarboxylic dianhydrides, it possible, and in fact advantageous, to use a large excess ofphthalic anhydride, for example or moles of phthalic anhydride per mole of benzene disulphony'lhalide "Thepolymers of the present invention are obtained by the direct, condensation of'the anhydride reactant with the polyarnine-reactant, but alternatively a polymer-forming derivative'of the anhydride, for example the correspending acid or a'partial ester and/or salt of the correspending-acid is used. These polymer-forming derivatives of ltheanhydride are well known to those skilled in the art. The polymers of "the invention referred to above as havinghigh'thermal' stabilities are polyimides, but the invention also includes polyamic acids formed by the condensation of the polyanhydride and the amine under mild reaction conditions. The polyamic acids are converted to polyimides on dehydration, and constitute a useful intermediate form of polyimide precursor.

"The polyamine monomeric components used in the present inventionare represented by the following genv r R(NH2)h (I) wherein R is an n-valent aromatic radical of from 2 to 52 carbon atoms. a

The polyamines used in the practice of the present invention include diamines characterized by the formula: R(NH -wherein R is a divalent radical containing at least two,carbon atoms selected from the following groups: aliphatic aromatic, cycloaliphatic, combination of aromatic and aliphatic, heterocyclic and bridged aromatic radicals ,whereinthe bridging group is a divalent radical selected-from the group consisting of alkylene of from 1 to 6 carbon atoms, oxygen, arylene of from 6 to 16; carbon atoms, --NI-I, sulfur, sulfonyl, carbonyl, phosphoroua; phosphonyl, silyl and derivatives thereof. The preferred R groups in the diamines are the aromatic amines containing at least one ring of 6 carbon atoms, characterized by benzenenoid unsaturation. Such R groupsinclude paraphenylene, meta-phenylene bisphenyl radicals, fused ring systems having 2 to 4 aromatienuclei, wherein the two amine groups would be located on separate aromatic nuclei and bridged organic radicals of the general formula:

UIMU phenylene diamine; 4,4 diamino biphenyl; 4,4' 7 di- 2,4 bis(rbeta: amino t butyl)toluene; bis (parabeta amino t butyl phenyl)ether; para bis (2- methyl 4 amino pentyl )benzene; para bis (1,1- dimethyl 5 amino pentyl)benzene; m-xylylene diamine;p-xylylene diamine; bis(para 4 amino cyclohexyl) methane; ethylenediamine, 1,3 propylenediamine; hexamethylene diamine; heptamethylene diamine; octamethylene diamine; nonomethylene diamine; decamethylene diamine; 3 methylheptamethylene diamine; 4,4 dimethylheptamethylene diamine; 2,11 diamino dodecane; 1,2- bis (3 amino propoxy)ethane; 2,2 dimethyl propylene diamine; 3 methoxy hexamethylene diamine; 2,5 dimethyl hexamethylene diamine; 2,5 dimethylheptamethylene diamine; S methylnonamethylene diamine; 1,4 diamino cyclohexane, 1,12 diamino octadecane; 2,5 diamino 1,3,4 oxadiazole; H N(CH )O(CH NH H N (CH NH 3,3 dichlorobenzidine; bis (4 amino phenyl)ethyl phosphine oxide; bis (4 amino phenyl) phenyl phosphine oxide; bis (4 amino phenyl)N phenylamine; p phenylene bis 2(amino 1,3 benzoxazole); 2,5 bis(p amino phenyl) 1,3,4 oxadiazole; mphenylene bis (m-aminobenzamide); 3,4 diamino benzanilde and mixtures of the foregoing. Other useful polyamino compounds include melamine, 4,4 thioaniline diphenyl ether, 4,4 diaminotriphenylamine, 1,2,4 triaminobenzene, polymethylene polyanilines made by reaction of aniline with formaldehyde which correspond to the following general formula:

NHz

n NHz (III) where m can be 1 to 4. 'Mixtures of these amines may be employed.

The polyamines illustrated in Formula III are prepared by the reaction of aniline and formaldehyde as is well known to those skilled in the art.

The general procedure for preparing these compounds is to react at least two (2) moles of aniline with one (1) mole of formaldehyde in the presence of an equivalent amount of concentrated hydrochloric acid. The aniline and hydrochloric acid are charged to a reaction vessel and formaldehyde (50%) is added at. temperaturesin the range of 50-90" C. The reactants are refluxed 'for aboutone hour at about 100 C,, after which time the batch is cooled to at least 40 C. Equivalent amounts of sodium hydroxide are added to' the batch. The layer containing the condensation product of the aniline and formaldehyde is then'washed and steam distilled to remove any unreacted aniline.

Additional procedures for preparing these components may be found-in U.S Pats. 2,974,168 and 2,818,433.

I NHz phthaloyl chloride phenylene diamine pyridine catalyst ambient temperature u @l l.

Another method involves the reaction of one mole of an aromatic diacyl halide with two moles of a monofunctional aromatic amine carrying a nitro-substituent, and subsequent reduction of the nitro groups, as is illustrated below:

om NH2 cap-4541 H2N- N02 0 o From the foregoing descriptions, those skilled in the art will readily recognize the methods and procedures used to prepare those compounds represented by Formulae III and IV above.

In a diamine having the two amino groups on a single aromatic nucleus, such groups preferably occupy positions other than the ortho, and in diamines having more than one aromatic nuclei, the two amino groups are preferably located in different nuclei.

Although in the aromatic diamines normally employed the amino groups are the only nuclear substituents, there may be present one or more additional inert nuclear substituents, for example alkyl groups or halogen atoms.

The polymers of the present invention are obtained by the direct condensation of the polyanhydride and the polyamine. The proportions of monomers can vary from about 25% excess of the polyanhydride to about 25% excess of the polyamine. Preferred are equivalent amounts of polyanhydride and amine or amounts that are substantially so. The reaction between the polyanhydride and the polyamine is carried out in the molten state or in a solvent medium.

Preferred solvents are polar liquids such as for instance the -N,N-di(lower alkyl) lower alkanolamides especially N,N-dimethylformamide and N,N-dimethylacetamide, N(lower alkyl)pyrrolidones, for example N- methylpyrrolidone, dimethyl sulphoxide, tetrahydrothiophene dioxide and hexamethylphosphoramide. Other solvents that can be used include lower alkyl alcohols of from 1 to 8 carbon atoms such as methanol, ethanol, etc., glycols such as ethylene glycol, propylene glycol; aminoalcohols such as N,N'-diethyl amino propanol; halogenated hydrocarbons, for instance chloroform, perchloroethylene and chlorobenene, and oxygen-containing solvents for example dioxane; ketones such as acetone, methyl ethyl ketone; ethers and esters.

The first stage reaction product, especially when operating at a relatively low temperature, for instance between 20 C. and 60 C., is a polyamic acid. Theconversion of this intermediate product to a thermally stable polyimide by the elimination of water between each amide grouping and its adjacent carboxylic acid grouping can be effected thermally or by the action of a chemical dehydrating agent. When heated alone, a temperature of at least C., for example from to 500 C. is generally required, temperatures in the range 200 to 400 C. being usual in practice. Dehydration can be effected at atmospheric pressure, but is advantageously conducted at reduced pressures. Chemical dehydrating agents that can be used include aliphatic acid anhydrides such as acetic anhydride, and carbodiimides. The solvent which may have been present during the formation of the polyamic acid will normally be removed before or during thermal dehydration, whereas chemical dehydrations requiring lower temperatures can often be conducted in the presence of the solvent.

In an alternative and preferred method for the production of the polymeric materials of the invention, the polyanhydride is first converted to a partial ester by reaction with a monohydric alcohol, generally one containing not more than 18, and preferably not more than 6 carbon atoms per molecule, for example methanol or ethanol, and the partial ester is then reacted with the amine. On subsequent heating, water and alcohol are eliminated to form imide linkages. The temperature required to effect this elimination is usually at least 100 C., for example from 150 to 500 C., and in practice temperatures of from ZOO-400 C. are most often employed.

The polyimide polymers of the invention are valuable as binding agents for use with fillers in the production of surface coatings, or with fillers or reinforcing materials, especially fibrous reinforcing materials, in the production of articles having high mechanical strengths. Where advantage is taken of the high thermal stabilities of the polymers, and the coating or article is intended for exposure to high temperatures, the filler or reinforcing material used is one which is itself refractory, for example silica, alumina, titania, zirconia, silicon carbide, or various aluminosilicates in powder form; or fibres or filaments of asbestos, silica, carbon, graphite, aluminum silicate, boron, boron nitride, refrasil, quartz, silicon carbide or glass.

In the production of such an article or coating, at least the final stages of the process during which imide groupings are formed to the extent that the polymer becomes substantially insoluble and infusible, are carried out in the pressure of the filler or reinforcing agent. The usual procedure involves the use of a'solution of polymer-forming components, for example a mixture of the polyanhydride and polyamine, a mixture of a polyanhydride partial ester and polyamine, a polyamic acid, a partial ester-amine salt or a resin having a limited content of imide'groupings consistent with its being soluble in the solvent. To obtain a high concentration of polymer-forming components in the solution it is sometimes advantageous to use a mixture of two or more of the various species. Suitable solvents include polar liquids such as N-alkyl-pyrrolidones especially N methylpyrrolidone, N,N dialkylcarboxamides, for instance. N,N-dirnethylforn1amide and N,N- dimethylacetamide, tetrahydrothiophene dioxide, dimethyl sulphoxideand hexar'nethylphosphoramide; and halogenated hydrocarbons, for example chloroform, perchloroethylene, and chlorobenzene.

The concentration of polymer-forming components in a solution for impregnation or coating is typically in the range 30-'50% by weight of the solution. The optimum, however, varies with the method of coating or the absorbency of the material to be impregnated. For example, where the coating is applied by spraying, or relatively thick sections of material are to be impregnated, more dilute and less viscous solutions containing for instance from 5 to 30% by Weight of polymer-forming components or less, may be appropriate. On the other hand,

solutions containing higher concentrations, for instance up to 75% by weight of polymer-forming components can be used for coatings that are applied by dipping.

In the usual procedure for the production of an article stitutes from 20 to 60% of this weight. For fibrous material of a given. absorbency, this ratio is determined largely by the concentration of polymer-forming components in the impregnating solution, which is selected accordingly. Preferred articles of high mechanical strengths have a laminated structure. Such' a structure can be formed by subjecting to pressure at polymerization temperatures an assembly of'several superimposed sheets or mats of impregnated fibrous material. Pressures of for example from 25 psi. to 750 p.s.i. or higher, for example up to 5000 p.s.i. and preferably from 50 to 600-p.s.i. can be used.

' The strengths of the laminates can often be further increased by the period of post-curing, during which the laminate is stored, usually at ordinary pressures, at an elevated temperature. The temperature of storage can for example be from 200376 C; and the duration from for example 12 to 200 hours.

Surface coatings can be applied using a melt or solution of polymer-forming components, and then cured by heating at a temperature at which polyimide formation occurs. A composition for use as a surface coating may be a varnish consisting essentially of a solution of polymer-forming components in an organic solvent, or it can contain a filler in finely-divided form. The filler can be one 'of those exemplified above, and typically has an average particle size in the range from millimicrons to 50 microns; The amount of filler can vary from, for example, up to 80% of the combined weight of polymer-forming components and filler; preferably this percentage lies in the range 10 to 75. Coating compositions may also contain dehydrating agents as exemplified above.

{In apreferred method of forming coatings, the surface, after the usual degreasing and cleaning, has applied to it one or two coatings of a varnish composition con- 10 as molding powders, electric insulation, films, fibers, and when foamed, as thermal insulation.

The invention is illustrated by the following examples.

EXAMPLE 1 This example is set forth to illustrate the preparation of a polyanhydride used as a starting material in the preparation of the polymers of the present invention using a molar ratio of sulphonyl halide/anhydride of 1/5 in the reaction mixture.

grams (0.29 mole) of m-benzenedisulphonyl chloride are added to a stirred, refluxing mixture of 215 grams (1.45 moles) of phthalic anhydride and 0.055 gram of copper in an atmosphere of nitrogen. The phthalic anhydride/copper mixture is heated to boiling point in a reaction vessel equipped with a stirrer, reflux condenser,

heated dropping funnel and an inlet for gas. A slow stream of nitrogen is led into the vessel above tho-surface of the liquid, and the m-benzenedisulphonyl chloride is added dropwise with stirring over a period of 6 hours 40 minutes, during which time the temperature rises from 284 C. to 298 C. Sulphur dioxide and hydrogen chloride are evolved and are led in the entraining stream of nitrogen into a scrubber containing sodium hydroxide solution. Analysis of the contents of the scrubber for chloride and sulphite at the end of the reaction showed that 97.3% of the theoretical amount of hydrogen chloride and 96.0% of the theoretical amount of sulphur dioxide has been evolved.

147 grams of unreacted phthalic anhydride are recovered by distillation of the reaction mixture at a pressure of 25 mm. of mercury, leaving 87.5 grams of product. From the amount of phthalic anhydride recovered, it is calculated that the polyanhydride product contains 77.7% by weight of units derived from the phthalic anhydride. The polyanhydride is characterized by having a plurality of direct aromatic nuclei to aromatic nuclei linkages.

EXAMPLE 2 This example is set forth to illustrate the preparation of the polymeric products of the present invention.

The polymer is obtained by grinding a mixture of 10 grams of the polyanhydride (0.0525 mole of anhydride units) prepared in Example 1 With 2.83 grams (0.026 mole) of p-phen-ylenediamine, to a fine powder and then transferring this ground mixture to a small flask fitted with a glass stirrer and thermometer. The mixture is heated and, after fusion, stirred. The mixture became progressively more viscous, and stirring is eventually discontinued. The temperature is taken to 300 C. for 30 minutes and the product is then allowed to cool. The polymeric product is a hard, insoluble, infusible resin, which contains a plurality of recurring imide linkages and direct aromatic nuclei linkages. This material has excellent oxidative thermal stability.

EXAMPLE 3 This example is set forth to illustrate the preparation of a six ply laminate wherein the cured impregnating resin is characterized by having a plurality of recurring imide linkages and direct aromatic nuclei to aromatic nuclei linkages.

'For the preparation of an asbestos-reinforced laminate, the half ester of the polyanhydride is first made by refluxing the polyanhydride for about 24 hours with an excess of anhydrous ethanol until solution is complete. An equivalent amount of p-phenylenediamine dissolved in ethanolis then added to the ester derivative and the resulting solution is used to impregnate six 6 inch by 4 inch asbestos felt mats. After draining and partial drying, these are laid one upon another and pressed for 3 minutes at 300 pounds per square inch and C., and 30 minutes at 300 pounds per square inch and 320 C. After post curing for 24 hours at 300 C. the laminate has high flexural strength and excellent thermal stability on aging in air at 300 C.

EXAMPLE 4 This example is set forth to illustrate the preparation of a polyanhydride having direct aromatic nuclei to aromatic nuclei linkages using a mole ratio of sulphonyl halide/anhydride of 1/ 12 in the reaction mixture.

The polyanhydride is obtained by a method essentially the same as that described in Example 1 using 3552 grams (24 moles) of phthalic anhydride (3,020 grams of which were recovered) and 550 grams (2 moles) of mbenzenedisulphonyl chloride in the presence of 12 grams of a copper powder catalyst. The polymeric product weighed 677 grams. From the amount of phthalic anhydride recovered, it is calculated that the product contains 78.6% by weight of phthalic anhydride units. By titration, the figure obtained for this proportion is 75.6%. A molecular weight determination in chloroform solution gives a value of 712.

EXAMPLE 5 This example is set forth here as another illustration of a multi-ply laminate wherein the cured impregnating resin is characterized by having a plurality of recurring imide linkages and direct aromatic nuclei to aromatic nuclei linkages.

1500 cc. of dry ethanol containing 630 grams of the polyanhydride prepared in Example 4 are boiled under reflux for 24 hours to give a solution of the half ester of the polyanhydride, to which is then added a solution in ethanol of the equivalent amount of m-phenylenediamine. Part of the resulting solution is used to impregnate six asbestos felts (12 inch x 12 inch) which are dried in air overnight and then for 2 hours at 50 C.

The felts are then placed one on top of another and pressed as follows: 15 minutes at 249 pounds per square inch and 120 C. and 5 hours at 311 pounds per square inch and 320 C. The laminate is post-cured for 24 hours at 300 C. when the resin content is found to be 49% (weight/weight).

The laminate has high fiexural strength and good aging properties at elevated temperatures.

EXAMPLE 6 This example describes the production of resins from a polyanhydride and a number of different diamines.

The polyanhydride used is obtained by a method essentially the same as that described in Example 1, with 45.9 grams (0.167 mole) of m-benzenedisulphonyl chloride being added over a period of 7 hours 40 minutes to 296 grams (2.0 moles) of stirred molten phthalic anhydride containing 0.05 gram of copper in the form of fine wire at a temperature of 288296 C. 252 grams of unreacted phthalic anhydride are recovered by distillation of the reaction mixture at a pressure of 25 mm. of mercury, leaving a product containing 78.25% by weight of units derived from the phthalic anhydride as calculated from the amount of phthalic anhydride recovered. A mixture of the polyanhydride and approximately twice its weight of dry ethanol is refluxed for 24 hours to give a solution of a partial ethyl ester of the polyanhydride. Portions of this solution are then treated as follows:

To one portion there is added an amount of p-phenylenediamine equivalent to the partial ester content of the solution. After mixing, the ethanol is evaporated under reduced pressure, and the residue is heated at 120 C. for 5 minutes, 320 C. for 3 hours and finally at 300 C. for 24 hours. The product after cooling is a hard, glassy resin.

An equivalent amount of meta-phenylenediamine is added to a second portion of the solution and the residue 12 after evaporation of the ethanol is heated at 160 C. for 5 minutes, at 325 C. for 5 hours and finally at 350 C. for 16 hours. The product after cooling is a hard, glassy resin.

A resin is obtained from a further portion of the solution of the partial ethyl ester and using an equivalent amount of ethylenediamine using the same procedure as for p-phenylenediamine in Part A above.

A rsein is obtained from a further portion of the solution of the partial ethyl ester and an equivalent amount of 4,4'-diaminodiphenyl ether using the same procedure as for p-phenylene diamine in Part A above.

Investigation of the thermal stabilities of the resins in the form of powder retained on a mesh BSS sieve but passing a 40 mesh BSS sieve, in air at 400 C. using a Stanton Thermobalance, shows that the resins prepared using an aromatic diamine have excellent thermal stability while that resin prepared from ethylenediamine had expectedly lower thermal stability. The polyimides from mand p-phenylene diamine lose weight less rapidly than that derived from 4,4'-diaminodiphenyl ether. The foregoing powders have utility as molding compositions.

EXAMPLE 7 This example describes the preparation of coating compositions and their use in coating metal surfaces wherein the cured coating compositions are characterized by having a plurality of recurring imide linkages and direct aromatic nuclei to aromatic nuclei linkages.

The polyanhydride starting material is obtained by a method essentially similar to that described in Example 1 using a m-benzene disulphonyl chloride and phthalic anhydride in a molar ratio of 1:6 in the reaction mixture. Excess phthalic anhydride is recovered giving a product containing 73.05% by weight phthalic anhydride units and having an equivalent weight of 101.0.

Part of the polyanhydride is converted to a solution containing 33.5% (w./v.) of the partial ethyl ester by refluxing with excess dry ethanol for 24 hours.

A solution is made having the following composition:

40 grams polyanhydride 32.5 cc. partial ester solution 13.4 grams p-phenylene diamine 350 cc. N-methylpyrrolidone The polyanhydride and the p-phenylenediamine are dissolved in separate portions of N-methylpyrrolidone, and the partial ester solution is added to the polyanhydride solution followed by the diamine solution.

Filled coating compositions are prepared by mixing portions of the above solution with an amount of filler equivalent to a percentage of the total solids content, i.e. polymer-forming components plus filler, as shown in the table below. The filler is incorporated by adding the solution slowly, with grinding, to the filler in a mortar.

The samples coated are mild steel (BSS 24) bars, 2 x x inches in size. These are treated before coating by boiling for 2 hours in chloroform, followed by pickling for 15-30 minutes in 12% aqueous hydrochloric acid containing 0.05% diphenylthiourea as an inhibitor. The bars are then washed and scrubbed with scouring powder, rinsed repeatedly with distilled water, then with a methylated spirits/acetone mixture, and are placed under chloroform until ready for use.

Coatings are formed by heating the bar and spraying it with the coating composition, the reservoir of which was shaken during spraying to maintain the filler in uniform suspension. Coating and cure conditions are shown in Table I below. Any intermediate coating that is not cured or partially cured is allowed to dry for approximately 15 minutes at the application temperature before applying the next coating.

Percent Applifiller of Total cation total number temp., Filler solids of coats C. Cure conditions xa it i 7 (A) Silica, 30 millimierons 25 120-140 1% hours at 300 C. 7(B) Silica, 8.8 microns 50 6 100-120 Every 2nd. coat. 7 (C). Silicon carbide, 12 microns. 50 6 100-120 D0.

v hour at 300 0. Finally 1% hours at 300 C.

The coatings are capableof withstanding prolonged exposure in air at elevated temperatures and show exceln f esistensst eq s ive v m e EXAMPLE 8 This example 'furthermillustrates, the use of polymers of the invention asbinding agents for various fibrous materials intthe product-ion of. laminates,

- The polyanhydride used'as starting material is obtained by'heating benzene m-disulphonyl chloridezphthalic anhydride-(mole-ratio of 1: 12) in the reaction mixture in a process essentially the same as that described for the production of the. polyanhydride of Example 1. The polyanhydride contains 75.5% by weight of phthalic anhydride units as determined by boiling a small sample of known weight for 30 minutes with an excess of N/ sodium hydroxide solution and then back-titrating the solution against-N/IO sulphuric acid.

1, A soluble ester of the polyanhydride is obtained by refluxing a mixture .of the polyanhydride and dry ethanol with stirring underanh-ydrous conditions for 16 hours. Approximately'15O cc of ethanol are used per 100 grams of polyanhydride. A solution for the impregnation of the fibrous reinforcing material is prepared by mixing the solution of the partial ester with a solution containing an equivalent weight of p-phenylenediamine in ethanol or chloroform and,distilling oifthe solvent until the con- ,centrate contains approximately 40% by weight of polymer-forming components. v

;;.Composites. containing carbon fibres as the reinforcing agent arevprepared by placing a weighed, 15 inch long bundle of fibres :in a trough and running the solution of polymer-forming components into the trough. After steeping, the tibrebundle is drained and dried at C. for 16 hours. After this period, the 15" x /2" impregnate is cut intofour 3.5" pieces, and these are weighed and aligned in the 3.5" long by /2". wide, by /2" deep well of a bar rnould. The pressing plate of the mould is placed in position and. the mould inserted between the hot platens of a press. Pressing is carried out in three stages, a warming up period with only touch pressure applied, a pre-press for a relatively short period at low pressure, followed by a main pressing at 'high temperature and pressure. Details are given in Table II below. The mould. is removed from the press after cooling to 250 C. in air, and to 100 C. With'watr, keeping the pressure constant. Post-cure is carried out by placnig the composite in an air circulating oven at 300 C. for 24 hours.

Other laminates are made using a cloth woven from fibre consisting essentially (98% by weight or above) of silica. Single 6" x 4" layers, of the cloth are placed on stainless steel gauze and impregnated with the solution of polymer-forming components. The impregnated cloths are dried at up to'50" C. for 16 hours and a sandwich of lZ'impregnated clot-hs is placed between aluminum foil (0.'004")'."This assembly is'placed in the press and the pressing' carrried out in two stages, a pre-press and a mainpress as shown in Table 11 below. The press was then cooled by airto 250 C. and by water to 100 C., keeping the pressure'constant, before removing .the laminate which is finally post-cured at 300 C. for 24 hours in an air-circulating oven.

A third type of laminate is made using a fibrous aluminosilgicate analyzing approximately 50% by weight A1 0 and 50% by weight SiO as the reinforcing agent. This was in the form of a felt or blanket of short, randomly-oriented fibres. Pieces 6" x 4" in size are used. Because of the thickness of the felt, the solution of polymerforming components is diluted before use to reduce its viscosity. The wet impregnates are dried at up to 50 C. for 17 hours. An assembly of 5 impregnates is then placed between aluminum foil (0.004") and the pressing carried out in two stages as before. The laminate is removed from the press after cooling under constant pressure to 250 C. with air and to C. with water and post-cured at 300 C. for 24 hours.

A fourth type of laminate is made using glass cloth as the reinforcing agent. The glass cloth used is satin weave having weft and warp strengths of the same order of magnitude, made from E glass fibre containing less than 1% of alkali, surface treated with methacryloyloxypropyl trimethoxy silane. An impregnating composition is prepared by adding to the solution of the partial ester described above a solution of an equivalent amount of mphenylenediamine in N-methyl-Z-pyrrolidone and distilling 01f the solvent (largely the ethanol) until a concentrate containing approximately 40% by weight of polymerforming components is obtained. Rectangles of cloth, 6" x 47 in size, are placed on stainless steel gauze and impregnated with the solution of polymer-forming components. The impregnated cloths are dried at C. for 17 hours, and a sandwich of 12 cloths is then placed between 2 sheets of 0.004" thick aluminum foil. This assembly is placed in a press, and the pressing carried out in two stages, a pre-press and a main press, as shown in the table below. The laminate is removed from the press after cooling in air to 250 C. under constant pressure, and further cooling to 100 C. with water. The laminate is postcured at 300 C. for 48 hours in an air-circulating oven. Further details are given in Table I I below.

Flexural strengths of the laminates are determined by cutting. test pieces approximately 3.5 inches long by 0.5 inch wide from the laminate using a diamond-tipped circular saw. After measuring the dimensions of a test piece accurately, it was suported' symmetrically across two parallel metal rods each 0.375 inch in diameter with axes 2 inches apart. A gradually increasing load is applied to the specimen through a third 0.375 inch diameter rod located parallel to, and equidistant and on the opposite side of the specimen from, the two supporting rods. The load required to break the specimen is measured and the flexural strength calculated from the formula:

' 1.5Xload 2 Flexural strength (psi) WE -fi where the load is expressed in pounds, 2 is the distance apart of the support rods in inches, and width and thickness are the width and thickness of the specimen in inches.

15 Table H follows below:

TABLE II.SUMMARY OF LAMINATES PREPARED IN EXAMPLE 8 Pressing conditions Laminate properties after post- Pro-press Main press Weight of curing laminate Tempera- Temperaafter Flexural ture, 'Iime, Press, ture, Time, Press, pressing, Percent, Thiekstrenght 0. minutes p.s.i. C. hours p.s.i. grams resin ness, p.s.

Reinforcing agent:

Carbon fibres 320 2 57 320 3. 133 342 3. 58 47. 25 0. 1055 48, 800 120 7 320 3 500 3. 40 46. 3 0. 1055 45, 650 120 l 100 320 1 100 40 17. 3 0. 092 13, 410 100 0. 5 25 320 1 100 57. 5 36. 85 0. 111 19, 300 70 O. 5 25 320 1 100 60. 5 38. 3 0. 118 14, 860

0.05 300 120 2 300 l 320 1. 0 935 85 47. 7 0. 137 15, 670 120 4 300 320 3 300 79 43. 7 0. 135 15, 080 350 5 Contact 350 0. 5 250 98 42 0. 103 48, 400

' 320 followed by.

EXAMPLE 9 the link between any two aromatic nuclei 1s a single A polyanhydride comparable to that of Example 1 is prepared and converted to the partial ethyl ester according to the procedures set forth in Example 8 above. The partial ester is mixed with an equivalent amount of 4,4- methylene dianiline to give a 7% solids solution in N- methyl pyrrolidone. This solution is filmed out on an aluminum sheet and baked for 2 hours at 160 C.; 10 minutes at 200 C.; 10 minutes at 250 C. and 5 minutes at 300 C.

The resulting film, which has a thickness of about 5 mils has an excellent apperance and good thermal stability.

EXAMPLE 10 Example 9 is repeated here except that an equivalent amount of 4,4-oxydianiline is substituted for the diamine used in Example 9. The resulting film has good thermal stability and better flexibility than the film of Example 9.

EXAMPLE 1 1 This example is set forth to illustrate the use of the polymers of the present invention as wire enamels. 64.5 parts of a polyanhydride (comparable to that prepared in Example 1 above); 15.2 parts of 2B ethanol and 337 parts of N-methyl pyrrolidone are added to a reaction flask. The temperature of the mixture is maintained between 50 to 60 C., with stirring for 8 hours and then cooled to about C. 32.8 parts of 4,4'-methylene dianiline is then dissolved in the partial ester solution. The solution is then filtered and is used to coat #18 copper wire in a wire tower application using a maximum temperature zone of 400 C. The coated wire is found to have good thermal stability.

As stated above the polymeric compositions of the present invention can be used as electrical insulation, thermal insulation, surface coatings, impregnating resins, structural adhesives, free films, foams, molding powders, etc.

This present invention contemplates the use of additives or adjuncts commonly used with polymeric compositions such as stabilizers, fillers, extenders, adhesion promoters, blowing agents, foaming agents, etc.

In view of the foregoing it is obvious that many deviations may be made in the products or processes set forth above without departing from the scope of this invention.

What is claimed is:

1. A composition of matter having a plurality of recurring imide linkages and direct aromatic nuclei to aromatic nuclei linkages, said composition comprising the polymeric reaction product of:

(A) a mixture of polycarboxylic anhydrides represented by the formula wherein D represents a radical derived by the loss of one or more hydrogen atoms from the nucleus of the phthalic anhydride molecule; E represents a radical[ derived by the loss of two or more hydrogen atoms nuclear carbon to nuclear carbon bond; and wherein the mixture of polycarboxylic anhydrides is prepared by heating a benzene disulphonyl halide with a molar excess of phthalic anhydride at temperatures in the range of from C. to 500 C. such that sulphur dioxide and a hydrogen halide are evolved and direct linkages are formed between carbon atoms of the nuclei that were originally the nuclei of the benzene disulphonyl halide and carbon atoms of the nuclei that were originally phthalic anhydride nuclei; and

(B) a diamine selected from the group consisting of M-phenylene diamine, p-phenylene diamine and diamine molecules which contain two benzene nuclei linked directly through a divalent radical selected from the group consisting of oxygen, sulphur, alkylene, haloalkylene, carbonyl and sulphonyl, and wherein the alkylene groups contain from 1 to 6 carbon atoms.

2. A composition of matter as in claim 1 wherein the ratio of D units to E units in the mixture of polycarboxylic anhydrides is from 1:2 to 2: 1.

3. A composition of matter as in claim 1 wherein the mixture of polycarboxylic anhydrides is prepared by heating the benzene disulphonyl halide with up to 10 moles of phthalic anhydride, per mole of benzene disulphonyl halide, at temperatures in the range of from 200 to 350 C. until evolution of sulphur dioxide and hydrogen halide is substantially complete.

4. The composition of matter of claim 1 wherein the diamine is selected from the group consisting of mphenylene diamine, p-phenylene diamine 4,4-methylene dianiline and 4,4-oxydi-aniline.

5. A composition of matter having a plurality of recurring imide linkages and direct aromatic nuclei to aromatic nuclei linkages, said composition comprising the polymeric reaction product of:

(A) a mixture of polycarboxylic anhydrides represented by the formula wherein D represents a radical derived by the loss of one or more hydrogen atoms from the nucleus of the phthalic anhydride molecule; E represents a radical derived by the loss of two or more hydrogen atoms from a benzene molecule; x is an integer of from 2 to 11 and y is an integer of from 1 to 10; wherein the link between any two aromatic nuclei is a single nuclear carbon to nuclear carbon bond; wherein the mixture of polycarboxylic anhydrides is prepared by heating a benzene disulphonyl halide with a molar excess of phthalic anhydride at temperatures in the range of from 200 C. to 350 C. such that sulphur dioxide and a hydrogen halide are evolved and direct linkages are formed between carbon atoms of the nuclei that were originally the nuclei of the benzene disulphonyl halide and carbon atoms of the nuclei that were originally phthalic anhydride nuclei; wherein the ratio of D units to E units in the mixture of polycarboxylic anhydrides is from 1:2 to 2:1; and

(B) a diamine selected from the group consisting of m-phenylene diamine, p-phenylenediamine and diamine molecules which contain two benzene nuclei linked directly through a divalent radical selected from the group consisting of oxygen, sulphur, alkylene, haloalkylene, carbonyl and sulphonyl and wherein the alkylene groups contain from 1 to 6 carbon atoms.

6. A composition as in claim 5 wherein the diamine is selected from the group consisting of m-phenylene diamine, p-phenylene diamine, 4,4'-methylene dianiline and 4,4-oxydi-aniline.

7. A composition of matter having a plurality of recurring polyamic acid groups and direct aromatic nuclei to aromatic nuclei linkages, said composition comprising the polymeric reaction product of:

(A) a mixture of polycarboxylic anhydrides represented by the formula wherein D represents a radical derived by the loss of one or more hydrogen atoms from the nucleus of the phthalic anhydride molecule; E represents a radical derived by the loss of two or more hydrogen atoms from a benzene molecule; x is an integer of from 2 to 11 and y is an integer of from 1 to wherein the link between any two aromatic nuclei is a single nuclear carbon to nuclear carbon bond; wherein the mixture of polycarboxylic anhydrides is prepared by heating a benzene disulphonyl halide with a molar excess of phthalic anhydride at temperatures in the range of from 200 C. to 350 C. such that sulphur dioxide and a hydrogen halide are evolved and direct linkages are formed between carbon atoms of the nuclei that were originally the nuclei of the benzene disulphonyl halide and carbon atoms of the nuclei that were originally phthalic anhydride nuclei; wherein the ratio of D units to E units in the mixture of polycarboxylic anhydrides is from 1:2 to 2:1; and

(B) a diamine selected from the group consisting of m-phenylene diamine, p-phenylenediamine and diamine molecules which contain two benzene nuclei linked directly through a divalent radical selected from the group consisting of oxygen, sulphur, alkylene, haloalkylene, carbonyl and sulphonyl and wherein the alkylene groups contain from 1 to 6 carbon atoms.

8. A composition as in claim 7 wherein the diamine is selected from the group consisting of m-phenylene diamine, p-phenylene diamine, 4,4'-methylene dianiline and 4,4'-oxydi-aniline.

9. A composition of matter comprising in admixture (A) alkyl ester derivatives of a mixture of poly carboxylic anhydrides wherein the alcohol moiety of the ester contains from 1 to 6 carbon atoms and wherein the polycarboxylic anhydrides are represented by the formula wherein D represents a radical derived by the loss of one or more hydrogen atoms from the nucleus of the phthalic anhydride molecule; E represents a radical derived by the loss of two or more hydrogen atoms from a benzene molecule; x is an integer of from 2 to 11 and y is an integer of from 1 to 10'; wherein the link between any two aromatic nuclei is a single nuclear carbon to nuclear carbon bond; wherein the mixture of polycarboxylic anhydrides is prepared by heating a benzene disulphonyl halide with a molar excess of phthalic anhydride at temperatures in the range of from 200 C. to 350 C. such that sulphur dioxide and a hydrogen halide is evolved and direct linkages are formed between carbon atoms of the nuclei that were originally the nuclei of the benzene disulphonyl halide and carbon atoms of the nuclei that were originally phthalic anhydride nuclei; wherein the ratio of D units to E units in the mixture of polycarboxylic anhydrides is from 1:2 to 2:1; and (B) a diamine selected from the group consisting of m-phenylene diamine, p-phenylene diamine and diamine molecules which contain two benzene nuclei linked directly through a divalent radical selected from the group consisting of oxygen, sulphur, haloalkylene, carbonyl and sulphonyl and wherein the alkylene groups contain from 1 to 6 carbon atoms. 10. The composition of claim 9 wherein the alcohol moiety of the ester is ethanol.

11. The composition of claim 9 which is dissolved in a solvent selected from the group consisting of N,N-dimethylformamide, N,N-dimethylacetamide, N methylpyrrolidone, ethanol, ethylene glycol and N,N'-diethylamino propanol.

12. The composition of claim 9 wherein the polyamine is selected from the group consisting of m-phenylene diamine, p-phenylene diamine, 4,4-methylene dianiline and 4,4-oxydianiline.

References Cited UNITED STATES PATENTS 3,179,634 4/ 1965 Edwards 26078 3,349,061 1 0/ 1967 Pruckmayr 26047 3,413,267 11/ 1968 Kreuz 260-47 WILLIAM H. SHORT, Primary Examiner L. L. LEE, Assistant Examiner US. Cl. X.R. 

